This invention relates to improvements in the production of industrial fabrics intended for use in covering power transmission belts, commonly referred to as V belts, and the like. Conventional belt cover fabrics, such as in U.S. Pat. Nos. 3,784,427 and 4,062,989 (the disclosures of which are incorporated by reference herein) have been generally suitable for performing their intended function for normal V belt life.
In such power transmission belt cover fabric constructions, the end of normal wear life is typically indicated when the cover fabric becomes abraded enough to show the undyed white filaments or fibers making up the yarns of the cover fabric. While this has been a safe practice, V belt manufacturers are presently applying dye to the tubular or square woven cover fabrics before coating to improve the cosmetic effect of the raw cut fabric edge along the belt. It is felt by some producers that transmission belt life is extended by dyeing the white fiber components of the cover fabric to a darker shade. This "cosmetic" treatment has the effect of extending the usage of the transmission belt--sometimes dangerously. This is because such cosmetic effects do not extend the wear life of the V belt, but tend to unduly prolong replacement because of the longer time needed to detect abraded fibers.
According to the present invention there is provided an improved method for making cover fabrics for V belts and the like. The cover fabric so produced exhibits greatly improved wear-life compared to prior art cover fabrics. The present invention also overcomes the possibly dangerous cosmetic effect associated with present cover fabrics, without adversely affecting the improved wear life properties of cover fabrics according to the present invention.
This increase in cover fabric wear-life is accomplished by impregnating the fiber bundle of the yarns making up the fabrics employed (typically bias cut woven tubular fabric, although knitted or non-woven fabrics may also be suitable), so as to coat or encapsulate the individual fibers thereof, for example by passing a continuous strip of bias cut woven fabric into a fluid mixture of an elastomeric polymeric material. The polymeric material is preferably dissolved or emulsified in a fluid mix having a relatively low viscosity in order to accomplish complete impregnation of the fiber bundle. The desired viscosity is about 2000 cps or less, and is preferably 1500 cps.+-.250 cps. Where pressurized or evacuated systems are available, or where exceptionally long paths in dip tanks are provided, complete impregnation can be achieved utilizing fluid mixes having viscosities somewhat higher than 2000 cps, and may be as high as 40,000 cps.
According to the present invention, the impregnating fluid mix also preferably includes a dark pigment, such as conductive black. One purpose of the pigment is to improve sales appeal by coloring the fibers to eliminate the objectionable whiteness of the raw cut edges of the fabric. However, this pigmenting effect is to be distinguished from dyeing. If dyeing is practiced, it is difficult to determine when abrasion of the fabric fibers has occurred, necessitating belt replacement.
According to the present invention, the impregnating and encapsulating polymeric materials holds the pigment on the fabric and fiber components until the pigment is abraded off with the coating. When such abrasion occurs, white fibers begin to show, signalling the time for belt replacement. Greater flex life and greater wear life is nevertheless achieved, because of the polymeric encapsulation of the individual fibers in the yarn bundle of the cover fabric, which protects such fibers from premature abrasion. Nevertheless, when there is serious abrasion the white fibers begin to appear, signalling that the belt is worn and should be replaced.
The fiber bundle impregnation according to the present invention is practiced by passing the continuous strip of bias cut fabric into a dip tank, and removing excess fluid mix by utilizing a pair of textile pad rolls. After impregnation the cover fabric is treated by following the conventional steps of U.S. Pat. Nos. 3,784,427 and 4,062,989. That is, an elastomeric coating is applied to the fabric strip, the strip is stretched in its width direction to increase the angular relation of the yarns or threads of the fabric relative to its longitudinal axis, and the thus coated strip is dried. There is usually no drying between impregnation and coating, although in some circumstances that may be feasible. After coating and drying, the continuous strip is longitudinally slit into a plurality of tapes, and the tapes are used for covering a V belt or the like.
It is therefore the primary object of the present invention to provide an improved cover fabric for V belts or the like, and a method of production thereof. This and other objects of the invention will become clear from the detailed description of the invention, and from the appended claims.